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Category:   Application (E-mail Server)  >   Postfix Vendors:
(Conectiva Issues Fix) Postfix Bounce Messages Let Remote Users Scan for Open Ports on Other Hosts
SecurityTracker Alert ID:  1007411
SecurityTracker URL:
CVE Reference:   CVE-2003-0468   (Links to External Site)
Date:  Aug 5 2003
Impact:   Host/resource access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 1.1.11 and prior versions
Description:   A vulnerability was reported in Postfix. A remote user can use a Postfix server to scan for open/closed ports on other hosts.

It is reported that a remote user can use a target Postfix server to conduct bounce scans of other hosts or denial of service attacks against other hosts.

A remote user can send a probing message to the following address (RCPT TO):


The target Postfix server will then attempt to connect to the specified port on the specified victim server. If the specified port is open, the target Postfix server will wait until the SMTP greeting timeout occurs before queueing the message. If the specified port if closed, the target Postfix server will immediately queue the message. By examining error messages eventually returned to the sender by the target Postfix server, the remote user (i.e., the sender) can determine which ports are open/closed on the specified victim server, according to the report.

The remote user can engage many Postfix servers to direct a large number of connections to a victim server to attempt a distributed denial of service attack.

Postfix versions 1.1.12 and 2.0 are reportedly not affected.

Impact:   A remote user can scan various hosts looking for open/closed ports using the Postfrix server as the scanning agent.

A remote user can attempt to conduct distributed denial of service attacks against various hosts using the Postfix server as the attack generator.

Solution:   Conectiva has released a fix.

Vendor URL: (Links to External Site)
Cause:   Access control error
Underlying OS:  Linux (Conectiva)
Underlying OS Comments:  7.0, 8

Message History:   This archive entry is a follow-up to the message listed below.
Aug 4 2003 Postfix Bounce Messages Let Remote Users Scan for Open Ports on Other Hosts

 Source Message Contents

Subject:  [conectiva-updates] [CLA-2003:717] Conectiva Security Announcement - postfix

Hash: SHA1

- --------------------------------------------------------------------------
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PACKAGE   : postfix
SUMMARY   : Remote denial of service vulnerability
DATE      : 2003-08-04 17:30:00
ID        : CLA-2003:717
RELEASES  : 7.0, 8

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 Postfix[1] is a widely used MTA (Mail Transport Agent, sometimes
 called just an email or SMTP server).
 This update for Conectiva Linux 7.0 and 8 fixes two vulnerabilities
 in Postfix reported[4] by Michal Zalewski:
 1. Postfix used as a bounce scanner (CAN-2003-0468)[2]
 By using specially created recipients, it is possible to make Postfix
 attempt to establish SMTP sessions with arbitrary hosts on arbitrary
 ports. This could be used to identify open TCP ports on remote
 machines or to just generate traffic.
 2. Remote denial of service (CAN-2003-0540)[3]
 A malformed address can be used to cause a denial of service
 condition in two ways:
 - by locking up the queue manager: the offending message has to be
 manually removed from the queue in order to restore the service;
 - by locking up the smtpd listener: when supplied with the malformed
 address, the listener process will stop responding. Multiple attacks
 in parallel will hang many smtpd processes, leading to a denial of
 In order to be vulnerable to this issue, the "append_dot_mydomain"
 paramater would have to be changed from the default value of "on" to
 Conectiva Linux 9 is not vulnerable to any of these issues since it
 ships with Postfix 2.0.x.

 All postfix users should upgrade their packages. The service will be
 automatically restarted after the upgrade if it was already running.


 The apt tool can be used to perform RPM packages upgrades:

 - run:                 apt-get update
 - after that, execute: apt-get upgrade

 Detailed instructions reagarding the use of apt and upgrade examples 
 can be found at

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All packages are signed with Conectiva's GPG key. The key and instructions
on how to import it can be found at
Instructions on how to check the signatures of the RPM packages can be
found at

- -------------------------------------------------------------------------
All our advisories and generic update instructions can be viewed at

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Copyright (c) 2003 Conectiva Inc.

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Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see



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